Why does the immune system respond to allergens by triggering itching in the skin?

Your skin is the first protective barrier against every pathogen and allergen in the world.

So, when your skin itches, you should know that it may have come into contact with something that’s harmful and causing this reaction. This primal, biological response involves not just the cells in your skin but the entire immune system.

Why allergens cause allergic reactions

According to Johns Hopkins Medicine, an allergic reaction that leads to itching begins in the immune system. When a substance your body is allergic to, like dust, mold or pollen, comes in contact with skin, it causes the immune system to react and produce antibodies that attack and eliminate the allergen. This reaction not only causes itching but can also present through other symptoms like wheezing, runny nose, watery or itchy eyes and sneezing.

A new study published in the journal Immunity explains the exact processes through which these allergic reactions occur.

The researchers behind this study start by pointing out that while the exact mechanism behind the immune response to pathogens was well understood by scientists, the knowledge about the immune response to allergens has been uncertain at best.

Allergic reactions like itching occur when the dendritic cells activate the T cells necessary to the release of antibodies but the exact steps and processes involved were unknown before this study.

The role of sensory nerves in allergic reactions

The study revealed that these dendritic cells, which act as the messengers between the innate and adaptive immune systems, are located right next to neurons that respond to allergies in the skin. These neurons are known as CD301b+ DCs (dendritic cells). When an allergen comes in contact with the skin, these dendritic cell neurons are activated and they release a neuropeptide known as substance P, which acts as both a neurotransmitter and a neuromodulator.

Substance P then directly takes the message from the dendritic cells to the lymph nodes. The lymph nodes activate the T cells in response, and the T cells then launch an attack against the invading allergen. The scientists also showed that these sensory neurons that release substance P are found in both isolated cell samples as well as complete living organisms like mice. These findings suggest that sensory neurons present in the skin play a huge role in the activation of the immune system in response to allergens.

The researchers further tested if chemically blocking the allergy-sensing dendritic cells in mice can stop the activation of allergic responses like itching. Success in stopping this activation would suggest that modulating this neural response pathway may help devise better therapies and medications for those who have seasonal allergies or severe allergic reactions.

This breakthrough study therefore not only provides better understanding of cell mechanisms involved in allergic reactions but also shares the platform on which future allergy therapies can be based.

For more information, read our article on Allergy . 

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